RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Friday 02 April 2004 09:41, Vivian Meazza wrote: The Spitfire also had a drag-reducing radiator. I think the key _was_ the wing section. The Spitfire was eventually fitted with a Mustang-like laminar flow wing, which enabled the aircraft to reach 450+ mph. Pardon my lack of aero-engineering experience, but aren't all wings built for laminar flow? Or does the term mean more laminar? The Mustang was one of the first aircraft to use an airfoil designed for longer runs of laminar flow. The Spit and FW190 did not - at least in the early versions. The upper surface of the wing should have been able to support a laminar flow with transition occurring as far back as half the wing chord. In practice, however, only the first 15% of the wing chord saw laminar flow, due to wing imperfections. [This, according to an article by aerodynamicist David Lednicer] Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
The Mustang was one of the first aircraft to use an airfoil designed for longer runs of laminar flow. The Spit and FW190 did not - at least in the early versions. The upper surface of the wing should have been able to support a laminar flow with transition occurring as far back as half the wing chord. In practice, however, only the first 15% of the wing chord saw laminar flow, due to wing imperfections. [This, according to an article by aerodynamicist David Lednicer] Jon Additionally [from Quest for Performance: The Evolution of Modern Aircraft], The use of the in-line engine of low frontal area resulted in a fuselage of relatively low total wetted area and gave the aircraft a lean, streamlined appearance. The low frontal area of the in-line engine was one of the chief advantages cited for this type of power plant; the disadvantage was the vulnerability of the cooling system to enemy fire. The aft location of the cooling radiator and its associated inlet and internal flow system is of interest. The system was designed with the objective of obtaining a net thrust from the cooling air as a result of heat addition from the engine coolant. This feature no doubt contributed to the very low drag coefficient of the aircraft. The P-51 was also the first aircraft to utilize the NACA laminar-flow airfoil sections, discussed earlier. Although it is doubtful that any significant laminar flow was achieved on production versions of the Mustang, the low-drag airfoils did provide improved characteristics at high subsonic Mach numbers. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Friday 02 April 2004 13:33, Jon Berndt wrote: [...] drag coefficient of the aircraft. The P-51 was also the first aircraft to utilize the NACA laminar-flow airfoil sections, discussed earlier. Although it is doubtful that any significant laminar flow was achieved on production versions of the Mustang, the low-drag airfoils did provide improved characteristics at high subsonic Mach numbers. How is the situation in this area today? Do for instance modern jet fighters have laminar flow over the whole wing? (I guess the whole picture changes a lot when you go supersonic.) -- best regards, Gunnstein Lye Systems engineer [EMAIL PROTECTED] | eZ systems | ez.no ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Gunnstein Lye wrote On Friday 02 April 2004 13:33, Jon Berndt wrote: [...] drag coefficient of the aircraft. The P-51 was also the first aircraft to utilize the NACA laminar-flow airfoil sections, discussed earlier. Although it is doubtful that any significant laminar flow was achieved on production versions of the Mustang, the low-drag airfoils did provide improved characteristics at high subsonic Mach numbers. How is the situation in this area today? Do for instance modern jet fighters have laminar flow over the whole wing? (I guess the whole picture changes a lot when you go supersonic.) I think that any aircraft designed post-1950 to operate in the trans-sonic region would have a laminar flow wing. For example: the De Havilland Venom was a Vampire with a laminar flow wing. Supersonic aerofoil sections are whole new subject. This may be of interest http://www.aae.uiuc.edu/m-selig/ads/aircraft.html That said that list shows a different NACA number for the Spitfire to a contemporary paper so ... Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Fri, 2 Apr 2004 00:39:34 -, Jim Wilson [EMAIL PROTECTED] wrote: snip Is it fair to say that the 400lbs of drag returns at approach speeds though? That number isn't apparent there. BTW YASim is reporting that the p51d is putting out about 2000 lb.+ maximum, which seems like a lot. I think that the article was referring to net thrust from the propellor-powerplant combination. 2000lb of engine ;power' doesn't necessarily make for 2000lb of thrust from the prop. I think its more that the drag returns, to some extent, when the engine is at lower power settings although, being a ramjet type arrangement, there may be a loss of efficiency (and hence higher drag) at lower speeds. Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Rick Ansell wrote: I think that the article was referring to net thrust from the propellor-powerplant combination. 2000lb of engine ;power' doesn't necessarily make for 2000lb of thrust from the prop. Actually, 2000 pounds of thrust doesn't sound that far off. To start with an intuitive argument: 2000 lbs is about half of what a light bizjet of the same weight as the Mustang gets, so we're not too far from the right ballpark. More numerically: The engine is listed as 1590 horsepower. Figure that it can develop that power at sea level while going at 360 knots (~180m/s). One HP is 745 watts, and figure about 80% efficiency (peak for most propellers is 85%) so we have: 1590 * 745 * 0.8 / 180 = 5264 Newtons == 1180 pounds of force. That's at max speed. If you develop the same power and get the same prop efficiency at 200 knots (which is still well within a normal environment), then you'll see 2000 pounds from the prop. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Thu, 1 Apr 2004 18:52:03 -0600, Jon Berndt [EMAIL PROTECTED] wrote: BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? I've got plenty of articles around here somewhere ... this sounds familiar. I'll see if I can find a reference. Some comparative numbers from WWII RAF (late 1943) testing. The Mustang was a P51B. Vs Spitfire IX: '... the Mustang is a much cleaner aircarft...' Wing Loading: 43.8 vs 31 lbs per sq ft Range with full fuel: 1.5 to 1.75 that of Spitfire Fuel Load: 183 vs 101 US Gal Oil: 13.3 va 7.5 US Gal Fuel with long range tanks: 330 vs 210 US Gal 20-30 mph faster at all heights. Heights for best performance: Similar, 10,000-15,00 ft and 25,000 to 30,000 ft Full power climb inferior: Spitfire formates with 5lb less boost with Mustang at full power. (full power in 18lbs boost) Climb at 175mph similar. Pulls away from Spitfire rapidly in a dive. Spitfire requires 4-6lbs more boost to remain in formation Inferior in turn. Turning circle not noticeably improved by flaps. Inferior in roll at normal speeds. Equivalent at 400 mph Vs Spitfire XIV Speed: No practical difference. Climb: Spitfire 'very much better' Dive: Advantage less marked than with Mk IX Vs FW190 A-3 (no water-methonol boost) Speed: c 50 mph faster than FW190, 70 mph above 28,000 ft. Climb: 'little to choose' Dive: Mustang can always out-dive FW190 Turn: Slightly superior. Roll rate: FW190 markedly better. Vs Bf109G-2 (no water-methonol of nitrous oxide) Faster at all heights. Bf109 best heights 16,000ft (Mustang 30 mph faster) and above 25,000 ft (30mph increasing to 50mph at 30,000 ft) Climb: Similar, Mustang slightly better above 25,000 ft, slightly worse below 20,000 ft Dive: Better in prolonged dive. turn: Mustang greatly superior. Roll: Not much to choose. In a tight turn the Bf109s wing slots open when a rapid change of bank is attempted producing an 'embarrassing' rate of roll. Wing tanks effect on performance: 40-50 mph loss of speed. Still faster than FW190 above 25,000 ft (but still slower than BF109). Climb: Out climbed by FW90 and Bf109. Followed by FW190, 'definitely outstripped' by Bf109 Dive: With 'fairly full' tanks still out dives FW190 and Bf109 turn: As tightly aa FW190, definitely better than Bf109 Roll: Handling very little effected. Vs Tempest V Speed: Mustang 15-20 mph slower up to 15,000 ft, same to 24,000 ft, Mustang 30 mph faster at 30,000 ft. Climbs 'Compare directly with speed tests' Rate of turn: Mustang slightly better Roll: Tempest V inferior. On power, the '1000 lb' quoted by Atwood probably referred to the P51A's powerplant, I don't have figures but the P51D may well have double the power. Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Fri, 2 Apr 2004 08:41:02 +0100, Vivian Meazza [EMAIL PROTECTED] wrote: snip The Spitfire also had a drag-reducing radiator. I think the key _was_ the wing section. The Spitfire was eventually fitted with a Mustang-like laminar flow wing, which enabled the aircraft to reach 450+ mph. it was to be known as the Spiteful. 373 aircraft were originally ordered from a revised Spitfire F21 contract although production was cancelled with the end of the war and the introduction into service of the new jet powered Meteor and Vampire. The aircraft eventually evolved into the Seafang for Royal Navy service which in its turn was also cancelled. The Spitfire radiator was fitted into the wing. The result was that a sharp turn in the duct was required. This produced turbulent flow through the radiator, largely negating the effect (there was _some_ benefit). Despite its other disadvantages the Spitfire wing had a higher compressibility threshold. Atwood made the point that, discounting losses due to production issues, the Mustang wing needed to be clean and polished to prevent a rapid drop off in efficiency - which didn't always apply in the field. This is one of the reasons why he regarded the radiator arrangement as more important. Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Fri, 2 Apr 2004 08:22:49 +0100, Vivian Meazza [EMAIL PROTECTED] wrote: Not only the clever radiator, but also the ejector exhausts ... They have both been exercising my mind recently. I think both could be modelled within the existing Yasim framework. They are both a source of additional thrust, and both have an associated drag penalty. From 'Combat Development in World War II: Fighter Aircraft': For a Spifire V changing from 'fishtail' to 'ejector' type exhausts improved maximum speed by 7 mph. Rubbing down, polishing and filing gaps gave 6 mph more, waxing 3 mph more. On the other hand, the contribution of both is marginal, I feel. I would be surprised if the radiator drag, or lack of it effected the overall behaviour of the P51d model. I think there is something bigger at work here - an incorrect entry in the Yasim file, or an FDM error. I suspect something to do with the propeller right now. IIRC Yasim doesn't model drag due to the prop yet. Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Jim Wilson wrote Vivian Meazza said: The P51d YASim file appears to have the following typo: wing ... flap1 start=0.543 end=0.94.5 lift=1.3 drag=1.4/ ^^ /wing Makes the model interesting in roll!! Hi Vivian, Someone more familiar with parser might know how this is read. Maybe as 0.94? In that case it wouldn't have any major affect on anything. This error has been in there a while. Yup, sorry, I was fiddling while trying to investigate the low power problem. The biggest problem I have with the p51d is that something seems to get into the flight model when you shut down the power and rpm (prop blade pitch) control. The aircraft seems to suddenly glide like something is going wrong in the fdm. Maybe it is my imagination, but it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Probably there are just some issues with modeling a piston/prop setup with the power of a merlin, but I'm concerned that something strange is happening at very low power settings. I have noticed the very same - it glided the whole length of the runway at 100 mph, and there was absolutely nothing that I could do to get the sped to come off. I was doing this as part of my research for the Spitfire IIa. A couple of queries: How are you doing the reduction gearing? I was wondering if the propeller cruise rpm number was right. According to the Spitfire data the _engine_ rpm at cruise was 2650 rpm. Should this number reflect the reduction gearing? Can the propeller pitch come off enough? Are you modelling a RH engine? My feeling is that we might not have the model of the interaction of the throttle and the constant speed prop quite right, or, more likely, I'm not using it right. Regards Vivian ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Vivian Meazza said: Jim Wilson wrote Vivian Meazza said: The P51d YASim file appears to have the following typo: wing ... flap1 start=0.543 end=0.94.5 lift=1.3 drag=1.4/ ^^ /wing Makes the model interesting in roll!! Hi Vivian, Someone more familiar with parser might know how this is read. Maybe as 0.94? In that case it wouldn't have any major affect on anything. This error has been in there a while. Yup, sorry, I was fiddling while trying to investigate the low power problem. The biggest problem I have with the p51d is that something seems to get into the flight model when you shut down the power and rpm (prop blade pitch) control. The aircraft seems to suddenly glide like something is going wrong in the fdm. Maybe it is my imagination, but it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Probably there are just some issues with modeling a piston/prop setup with the power of a merlin, but I'm concerned that something strange is happening at very low power settings. I have noticed the very same - it glided the whole length of the runway at 100 mph, and there was absolutely nothing that I could do to get the sped to come off. I was doing this as part of my research for the Spitfire IIa. A couple of queries: How are you doing the reduction gearing? I was wondering if the propeller cruise rpm number was right. According to the Spitfire data the _engine_ rpm at cruise was 2650 rpm. Should this number reflect the reduction gearing? Can the propeller pitch come off enough? Are you modelling a RH engine? My feeling is that we might not have the model of the interaction of the throttle and the constant speed prop quite right, or, more likely, I'm not using it right. Typically this kind of problem in YASim indicates a lack of thrust to attain the cruise performance figures. There is something that isn't quite right though. After the gear reduction code went in I tried adjusting some of the numbers and always just ended up with less thrust and much worse results. At the time I didn't have more than a few minutes to play around with it so I reverted to running without the reduction number. I don't recall what RH is off hand. This is the Merlin 1650 with the 2 stage super charger (IIRC it is super not turbo). Possibly the weakness has something to do with the modeling of the boost, or that much boost. If you are interested in the behavior of the manual rpm control interaction take a look at the YASim patches I submitted on this about a year ago. Also you can study some of the effects by watching the engine/thrust property value while you make adjustments in flight. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Thu, 1 Apr 2004 04:14:23 -, Jim Wilson [EMAIL PROTECTED] wrote: Hi Vivian, Someone more familiar with parser might know how this is read. Maybe as 0.94? In that case it wouldn't have any major affect on anything. This error has been in there a while. The biggest problem I have with the p51d is that something seems to get into the flight model when you shut down the power and rpm (prop blade pitch) control. The aircraft seems to suddenly glide like something is going wrong in the fdm. Maybe it is my imagination, but it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Probably there are just some issues with modeling a piston/prop setup with the power of a merlin, but I'm concerned that something strange is happening at very low power settings. This possibly a side effect of trying to match the low effective drag at speed of the Mustang. At higher throttle settings the radiator oil cooler assembly (in that 'hump' under the aircraft) is set up to operate a little like a jet engine. IIRC this offsets around 80% of the drag due to the radiator/oil cooler. At lower power settings you get the drag back. I don't think Yasims solver is set up to account for this sort of strange behaviour. Sorry to bang on about one of my hobby-horses again! Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Rick Ansell wrote: I don't think Yasims solver is set up to account for this sort of strange behaviour. It's not, but then again it's also not set up to model some much more important power effects, like prop wash on the control surfaces. You hear about this magical radiator design an awful lot; I kinda have to wonder if it's mostly a myth. Are there any numbers on this thing? Jim Wilson wrote earlier: it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Are you sure you're above ground effect height? The Mustang has a big wingspan, and sits relatively low on its gear. It will definitely have a much higher ground effect threshold than the other piston engine planes will. Andy ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Thu, 01 Apr 2004 14:18:08 -0800, Andy Ross [EMAIL PROTECTED] wrote: Rick Ansell wrote: I don't think Yasims solver is set up to account for this sort of strange behaviour. It's not, but then again it's also not set up to model some much more important power effects, like prop wash on the control surfaces. You hear about this magical radiator design an awful lot; I kinda have to wonder if it's mostly a myth. Are there any numbers on this thing? You probably hear about it a lot on this list because of me! (Lurking around in the background and starting to build the skills he needs to make the contributions he wants to). I have, somewhere, an article on the P51 which has elements of an interview with the designer wherin he refers to this effect. IIRC he stated 80% of drag due to radiator and oil cooler removed at full power. IIRC there were a few other numbers. I think this makes it 'not a myth'. The designer (can't remember the name ATM) also said that the Germans had captured an essentially intact aircraft and Kurt Tank had spent many hours of wind tunnel time trying to work out why the P51 had the range and speed it did. Without detailed powered models he never did. I did suggest a while back the use of a small air brake surface, (omitted from the visual model) slaved to retract as the throttle lever was advanced as a simple way of representing this effect. It would be better to slave to rpm (or, even better, engine temperature, with a lag, if you want a challenge!) though. Could anything like this be done with Yasim as it stands? BTW i'm not 'having a go' at Yasim or any other part of FlightGear, just trying to help in a small way. This is, as I say, pretty much a 'one off case' and I wouldn't expect taking account of it to be a priority for incorporation in Yasim. Meanwhile I'll get back in my box and go back to the mysteries of Mil Std 2525B (as updated) symbology. Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Andy Ross said: Jim Wilson wrote earlier: it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Are you sure you're above ground effect height? The Mustang has a big wingspan, and sits relatively low on its gear. It will definitely have a much higher ground effect threshold than the other piston engine planes will. Well I don't have an exact number right now. If you get a chance take it for a spin, because I'm not really 100% sure of my observations. It seems like more than could (or should) be accounted for by ground effect modeling anyway. As for the thrust from the oil cooler, I'm skeptical of that as well. Estimates I've seen have been more modest anyway. This article might account for the 80% figure since it's reference claims that the p51d duct design reduce cooling system drag by 7/8 (not the aircraft drag!). This article is about models but the first five paragraphs deal with the real world reference: http://www.mfarchive.modelstuff.co.uk/mf073/airspace.htm Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Thu, 1 Apr 2004 22:59:03 -, Jim Wilson [EMAIL PROTECTED] wrote: snip As for the thrust from the oil cooler, I'm skeptical of that as well. Estimates I've seen have been more modest anyway. This article might account for the 80% figure since it's reference claims that the p51d duct design reduce cooling system drag by 7/8 (not the aircraft drag!). This article is about models but the first five paragraphs deal with the real world reference: http://www.mfarchive.modelstuff.co.uk/mf073/airspace.htm That looks like a portion of the same article. Atwood began by saying that the wing wasn't the key, as often supposed. BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? Rick -- Help the Waterway Recovery Group to help restore the Uks canal network Make a donation to the 'Right Tool' Appeal http://www.wrg.org.uk/cgi-bin/fmaker.pl?appeal.htm ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Rick Ansell said: On Thu, 1 Apr 2004 22:59:03 -, Jim Wilson [EMAIL PROTECTED] wrote: snip As for the thrust from the oil cooler, I'm skeptical of that as well. Estimates I've seen have been more modest anyway. This article might account for the 80% figure since it's reference claims that the p51d duct design reduce cooling system drag by 7/8 (not the aircraft drag!). This article is about models but the first five paragraphs deal with the real world reference: http://www.mfarchive.modelstuff.co.uk/mf073/airspace.htm That looks like a portion of the same article. Atwood began by saying that the wing wasn't the key, as often supposed. BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? Is it fair to say that the 400lbs of drag returns at approach speeds though? That number isn't apparent there. BTW YASim is reporting that the p51d is putting out about 2000 lb.+ maximum, which seems like a lot. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
On Friday 02 April 2004 01:39, Jim Wilson wrote: Rick Ansell said: On Thu, 1 Apr 2004 22:59:03 -, Jim Wilson [EMAIL PROTECTED] wrote: snip As for the thrust from the oil cooler, I'm skeptical of that as well. Estimates I've seen have been more modest anyway. This article might account for the 80% figure since it's reference claims that the p51d duct design reduce cooling system drag by 7/8 (not the aircraft drag!). This article is about models but the first five paragraphs deal with the real world reference: http://www.mfarchive.modelstuff.co.uk/mf073/airspace.htm That looks like a portion of the same article. Atwood began by saying that the wing wasn't the key, as often supposed. BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? Is it fair to say that the 400lbs of drag returns at approach speeds though? That number isn't apparent there. BTW YASim is reporting that the p51d is putting out about 2000 lb.+ maximum, which seems like a lot. Best, Jim I wonder if it might improve the area-rule characteristics - does it fly fast enough for it to be significant? LeeE ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? I've got plenty of articles around here somewhere ... this sounds familiar. I'll see if I can find a reference. Jon ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Rick Ansell wrote Hi Vivian, Someone more familiar with parser might know how this is read. Maybe as 0.94? In that case it wouldn't have any major affect on anything. This error has been in there a while. The biggest problem I have with the p51d is that something seems to get into the flight model when you shut down the power and rpm (prop blade pitch) control. The aircraft seems to suddenly glide like something is going wrong in the fdm. Maybe it is my imagination, but it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Probably there are just some issues with modeling a piston/prop setup with the power of a merlin, but I'm concerned that something strange is happening at very low power settings. This possibly a side effect of trying to match the low effective drag at speed of the Mustang. At higher throttle settings the radiator oil cooler assembly (in that 'hump' under the aircraft) is set up to operate a little like a jet engine. IIRC this offsets around 80% of the drag due to the radiator/oil cooler. At lower power settings you get the drag back. I don't think Yasims solver is set up to account for this sort of strange behaviour. Sorry to bang on about one of my hobby-horses again! Not only the clever radiator, but also the ejector exhausts ... They have both been exercising my mind recently. I think both could be modelled within the existing Yasim framework. They are both a source of additional thrust, and both have an associated drag penalty. On the other hand, the contribution of both is marginal, I feel. I would be surprised if the radiator drag, or lack of it effected the overall behaviour of the P51d model. I think there is something bigger at work here - an incorrect entry in the Yasim file, or an FDM error. I suspect something to do with the propeller right now. Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
RE: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Rick Ansell wrote On Thu, 1 Apr 2004 22:59:03 -, Jim Wilson [EMAIL PROTECTED] wrote: snip As for the thrust from the oil cooler, I'm skeptical of that as well. Estimates I've seen have been more modest anyway. This article might account for the 80% figure since it's reference claims that the p51d duct design reduce cooling system drag by 7/8 (not the aircraft drag!). This article is about models but the first five paragraphs deal with the real world reference: http://www.mfarchive.modelstuff.co.uk/mf073/airspace.htm That looks like a portion of the same article. Atwood began by saying that the wing wasn't the key, as often supposed. BTW I never said 'whole aircraft drag' - always just the drag due to the cooling system. In this article we have some better numbers: 350lb of additional thrust on an aeroplane generating c. 1000lb of thrust via the prop. Or 400lbs worth of drag reduced to 50lbs. The Spitfire MkIX wasn't a particularly inefficient aeroplane, there has to be a reason why the Mustang (unquoted Mk but assumed to be roughly equivalent) was (according to this article) 30mph faster. Wing, duct or both? Rick The Spitfire also had a drag-reducing radiator. I think the key _was_ the wing section. The Spitfire was eventually fitted with a Mustang-like laminar flow wing, which enabled the aircraft to reach 450+ mph. it was to be known as the Spiteful. 373 aircraft were originally ordered from a revised Spitfire F21 contract although production was cancelled with the end of the war and the introduction into service of the new jet powered Meteor and Vampire. The aircraft eventually evolved into the Seafang for Royal Navy service which in its turn was also cancelled. Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
[Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
The P51d YASim file appears to have the following typo: wing ... flap1 start=0.543 end=0.94.5 lift=1.3 drag=1.4/ ^^ /wing Makes the model interesting in roll!! Regards Vivian Meazza ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
Re: [Flightgear-devel] FGFS 0.9.4 - Aircraft Data - P51d
Vivian Meazza said: The P51d YASim file appears to have the following typo: wing ... flap1 start=0.543 end=0.94.5 lift=1.3 drag=1.4/ ^^ /wing Makes the model interesting in roll!! Hi Vivian, Someone more familiar with parser might know how this is read. Maybe as 0.94? In that case it wouldn't have any major affect on anything. This error has been in there a while. The biggest problem I have with the p51d is that something seems to get into the flight model when you shut down the power and rpm (prop blade pitch) control. The aircraft seems to suddenly glide like something is going wrong in the fdm. Maybe it is my imagination, but it seems like I'll get the thing nicely trimmed for landing so that you have to apply a little power to keep it on approach and above stall speed. It feels right. Then once I get above the runway (still above ground effect height), it just glides much too well with all power shut down to idle. Probably there are just some issues with modeling a piston/prop setup with the power of a merlin, but I'm concerned that something strange is happening at very low power settings. Best, Jim ___ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
